# std::pmr::polymorphic_allocator<T>::polymorphic_allocator

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< cpp‎ | memory‎ | polymorphic allocator

polymorphic_allocator() noexcept; | (1) |
polymorphic_allocator( const polymorphic_allocator& other ) = default; | (2) |
template< class U > polymorphic_allocator( const polymorphic_allocator<U>& other ) noexcept; | (3) |
polymorphic_allocator( std::pmr::memory_resource* r ); | (4) |

Constructs a new `polymorphic_allocator`.

1) Constructs a `polymorphic_allocator` using the return value of std::pmr::get_default_resource() as the underlying memory resource.
2,3) Constructs a `polymorphic_allocator` using other.resource() as the underlying memory resource.
4) Constructs a `polymorphic_allocator` using r as the underlying memory resource. This constructor provides an implicit conversion from std::pmr::memory_resource*.

### Parameters

other | - | another `polymorphic_allocator` to copy from
r | - | pointer to the memory resource to use. May not be null

### Exceptions

4) Throws nothing.

### Notes

Copying a container using a `polymorphic_allocator` will not call the allocator's copy constructor. Instead, the new container will use the return value of `select_on_container_copy_construction` (a default-constructed `polymorphic_allocator`) as its allocator.

### See also

select_on_container_copy_construction | create a new `polymorphic_allocator` for use by a container's copy constructor (public member function)

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